In particular in automotive vehicle construction, but also in other application fields, for example aircraft construction or rail vehicle construction, metal sheets of aluminium alloy are required which are not only distinguished by particularly high strength values, but at the same time have a very good formability, and which enable high degrees of deforming. In automotive vehicle construction, typical application fields are the bodywork and chassis components. In the case of visible painted components, for example metal bodywork sheets which are visible from the outside, additionally the forming of the materials has to be carried out in such a manner that after painting, the surface appearance is not impaired by defects such as flow figures or roping. This is for example particularly important for the use of aluminium alloy sheets for production of bonnets and other bodywork components of an automotive vehicle. However, the choice of materials is restricted with regard to the aluminium alloy. In particular AlMgSi alloys, the main alloy constituents of which are magnesium and silicon, have relatively high strengths in state T6 with, at the same time, good formability in state T4, and excellent corrosion resistance. AlMgSi alloys are alloy types AA6XXX, for example alloy type AA6016, AA6014, AA6181, AA6060 and AA6111. Conventionally, aluminium strips are produced from an AlMgSi alloy by casting of a rolling ingot, homogenising of the rolling ingot, hot rolling of the rolling ingot and optional cold rolling of the hot strip. The homogenisation of the rolling ingot is carried out at a temperature of 380 to 580° C. for more than one hour. Owing to a final solution annealing operation at a typical temperature of 500 to 570° C. with subsequent quenching and natural ageing at around room temperature for at least three days, the strips can be delivered in state T4. State T6 is set after quenching, by means of artificial ageing at temperatures between 100° C. and 220° C.
It is problematic that, in hot-rolled aluminium strips of AlMgSi alloys coarse Mg2Si precipitations are present, which are broken and comminuted in the subsequent cold rolling due to the high degrees of forming. Hot strips of an AlMgSi alloy are usually produced in thicknesses of 3 to 12 mm and supplied to cold rolling with high forming strains. Since the temperature range in which the AlMgSi phases are formed is passed very slowly in conventional hot rolling, namely after coiling of the hot strip, these phases form very coarsely. The temperature range for forming the above phases is alloy-dependent. However, it lies between 550 and 230° C., i.e. in the range of the hot-rolling temperatures. It could be proven experimentally that these coarse phases in the hot strip have a negative influence on the elongation of the end product. This means that the formability of aluminium strips made of AlMgSi alloys could previously not be fully exploited.
In the published European patent application EP 2 270 249 A1, belonging to the same Applicant, the AlMgSi alloy strip has a temperature of maximum 130° C. directly after exiting from the last hot-rolling pass and is coiled with this or a lower temperature. By quenching the hot strip in this method, aluminium strips can be produced in state T4, which in state T4 have an elongation at break A80 of over 30% or a uniform elongation Ag of more than 25%. In addition in state T6, very high values for the uniform elongation Ag and elongation at break A80 were achieved. In the said application fields, however, in addition the problem arises that frequently tight bends and flanging are required. A typical application comprising bending and flanging and high requirements for formability is for example an inner door panel of a motor vehicle. Although good results were achieved in bending tests with former AlMgSi alloy strips, but a further improvement of the bending behaviour, in particular taking into account the said application, would be desirable.
On this basis, the present invention faces the object of producing a strip consisting of an aluminium material for production of components with high forming requirements, which strip has an improved bending behaviour.